Installation structure for RFID tag, method for installing RFID tag, and communication using such RFID tag

ABSTRACT

An RFID tag installing structure for installing a microminiaturized RFID tag having a cylindrical antenna coil to a conductive member, an RFID installing method, and communication method are disclosed. An RFID tag ( 1 ) having a cylindrical antenna coil ( 2 ) and shaped into a rod is characterized in that the axial direction of the RFID tag ( 1 ) is parallel to the installation surface composed of the bottom surface ( 7   a ) of an installation groove ( 7 ) made in a conductive member ( 5 ) and is in contact with the installation surface.

CROSS-REFERENCE TO RELATED APPLICATION

The entire disclosure of Japanese patent application No. 2000-215935filed on Jul. 17, 2000; and No. 2000-268241 filed on Sep. 5, 2000,including the specification, claims, accompanying drawings and abstractof the disclosure is incorporated herein by reference in its entirety,in order to claim priority right according to 35 U.S.C. §119.

1. Field of the Invention

The present invention relates to an installation structure and aninstallation method in which an RFID having an antenna coil and acontrol section is installed to a conductive member, and a communicationmethod using such tag.

2. Description of the Related Art

Conventional RFID (Radio Frequency IDentification) tags are roughlyclassified into those of the electromagnetic induction type and theelectromagnetic coupling type; both of which are designed to communicatein a non-contact manner with a read/write terminal or so usingelectromagnetic wave.

The RFID tag has an antenna coil and a control section, in which asignal sent from the read/write terminal is received by the antennacoil, converted by the control section into an electric power and storedin a capacitor, and using such electric power the antenna coil sendsinformation such as an ID code stored in a memory section back to theread/write terminal.

There are two representative send/receive systems—ASK system and FSKsystem; where the send/receive operation of the former is based onamplitude shift keying, and the latter on frequency shift keying.

The antenna coils of the general RFID tags can be classified by typesinto those having a disk shape using a circular air-core coil, and thosehaving cylindrical shape using a ferrite core rod and enameled wirewound around such core. The appearances of these tags depend on theshapes of the individual antenna coils, that is, the former appears as adisk, and the latter as a rod.

The RFID tag having a disk-shaped antenna coil performs communicationbased on changes in magnetic flux in the in-plane direction of acircular coil, and the RFID tag having a cylindrical antenna coilperforms communication based on changes in magnetic flux in the axialdirection of such tag.

Electromagnetic wave can now be referred as alternating electric fieldand magnetic field simultaneously propagating while being oscillating inplanes normal to each other. When alternating magnetic flux ascribableto changes in the magnetic field is intersected by a conductive membersuch as those made of iron, aluminum or copper, such conductive memberinternally generates eddy current, and such eddy current generatescounter magnetic flux in a direction canceling such alternating magneticflux.

Hence, it has been a general practice to install the RFID tag apart aspossible from the conductive member.

However for the case that the RFID tag has to be, by all means,installed in the vicinity of a conductive member, a possible measure issuch that placing an RFID tag having the foregoing disk-shaped antennacoil so that the coil plane thereof is aligned in parallel to thesurface of the conductive member, while being interposed with anon-conductive spacer so as to bring the tag apart from such conductivemember to thereby suppress the generation of eddy current; or such thatproviding a material having a large magnetic permeability, such as aferrite core or an amorphous magnetic material sheet, between the coilplane and the conductive member so as to direct magnetic flux possiblyleaks through such conductive member toward the material having a largemagnetic permeability to thereby suppress the generation of eddycurrent.

These methods are successful in reducing effects of the magnetic member,and any of these methods can perform communication in the directionnormal to the coil plane, that is, the direction the magnetic flux fromthe disk-shaped antenna coil distributes.

On the other hand, an RFID tag having a cylindrical antenna coil is farmore size-reducible than an RFID tag having a disk-shaped antenna coil,and is thus excellent in adoptability in various applications.

It has, however, been considered as principally difficult to install theRFID tag having a cylindrical antenna coil onto the surface of aconductive member, so that such installation has not been practiced.

As has been described in the above, the RFID tag having a cylindricalantenna coil generates magnetic flux along the axial direction of suchantenna coil, so that it is advantageous in terms of sensitivity toperform communication with a read/write terminal from the tip of a coremember inserted into such antenna coil.

According to such consideration, installation of such tag onto thesurface of a conductive member must be such that aligning the axialdirection thereof normal to the surface of the conductive member tofacilitate the communication. This requires the conductive member tohave in a surface portion thereof a vertical installation hole(installation groove), in which the RFID tag is installed vertically.

Communication between a read/write terminal and the RFID tag installedin such installation hole having a conformable size may, however, bedisabled being adversely affected by the conductive member surroundingthe tag. This is why the conventional technique has employed the RFIDtag having a disk-formed antenna coil for the case it should beinstalled onto the surface of a conductive member.

SUMMARY OF THE INVENTION

The present invention is to solve the foregoing problems, and an objectthereof resides in providing an installation structure and aninstallation method of RFID tag, which allows the RFID having acylindrical antenna coil extensively reducible in size to be installedto a conductive member, and a communication method using such tag.

The present inventors found out after extensive investigations thatcommunication with an RFID tag is enabled using magnetic flux extendingin a space over the installation plane thereof if the RFID tag has arod-shaped cylindrical antenna coil and is installed so as to direct thelongitudinal direction (axial direction) thereof in parallel to theinstallation plane of a conductive member, and so as to approximatelycontact with such installation plane, which led them to complete thepresent invention.

That is, an installation structure for an RFID tag as set forth inembodiments is such that installing an RFID tag having an antenna coiland a control section to a conductive member, in which the RFID tag hasa cylindrical antenna coil to thereby have as a whole a rod shape, andis installed so as to direct the axial direction thereof in parallel tothe installation plane of said conductive member, and so as toapproximately contact with such installation plane.

According to such constitution, a part of the magnetic flux goes outfrom the tip of the cylindrical antenna coil and extends along the axialdirection thereof penetrates into the conductive member. While the totalmagnetic flux may slightly decrease depending on eddy current generatedwithin such conductive member, a part of the residual magnetic fluxpenetrates the RFID tag and runs in a space over the installation planeof the conductive member to form closed loops. The communication with anexternal read/write terminal or the like is enabled while being mediatedby such magnetic flux.

Even when the conductive member can afford only a very small space forinstalling the RFID tag, a highly size reducible RFID tag can readily beinstalled.

This also promises an excellent operability in the communication, sincethe communication is performed while being mediated by the magnetic fluxpenetrating the RFID tag and extending over the installation plane ofthe conductive member.

In such installation structure, the conductive member may have in thesurface portion thereof a top-opened installation groove, in which theRFID tag can be installed so as to direct the axial direction thereof inparallel to the installation plane comprising the bottom plane of suchgroove. Such constitution allows the RFID tag to be installed stably tothe conductive member, and also allows communication mediated by themagnetic flux which penetrates the RFID tag and extends in a space overthe installation plane of the conductive member.

In either one of the foregoing installation structures, the RFID tag maybe installed so as to keep a distance of 10 μm to 5 mm away from theinstallation plane of the conductive member. This successfully reducesaffection by the conductive member to thereby sensitize thecommunication.

Limiting the distance between the RFID tag and the installation plane ofthe conductive member to 5 mm or below can successfully reduce theamount of projection of the RFID tag out from the surface of theconductive member, or reduce the depth of the installation groove formedin the conductive member. This ensures retainment of properties andstrength of the conductive member.

An installation structure for an RFID tag as set forth in embodiments issuch that installing an RFID tag having an antenna coil and a controlsection to a conductive member, in which the conductive member has inthe surface portion thereof an installation groove, the RFID tag has acylindrical antenna coil to thereby have as a whole a rod shape, andsuch tag is installed so as to direct the axial direction thereofoblique to the bottom plane of the installation groove.

According to such constitution, a projected installation area on theconductive member can further be shrunk as compared to that attainablein other embodiments The magnetic flux can propagate into a space formedaside the tag within the installation groove, and then leak out from theinstallation groove, which successfully mediates the communication witha read/write terminal.

In either one of the foregoing installation structures, the RFID tag inan installed state within the installation groove may be protected onthe lateral plane and/or plane opposing to the installation planethereof with a protective member made of a conductive material. Thisensures more reliable protection of the RFID tag.

In the foregoing installation structure, the protective member can beprovided with a top-opened housing portion in the surface portionthereof, and the RFID tag can be housed within such housing portion tothereby protect the lateral plane and/or plane opposing to theinstallation plane of such tag. This allows precise positioning andinstallation of the RFID tag with the aid of the protective member.

In either one of the foregoing installation structures, the surface sideof the RFID tag installed to the conductive member may be covered with aprotective member made of a non-conductive material. This effectivelyprotects the RFID tag from external stress, impact or outer environment.

In either one of the foregoing installation structures, the RFID tag maybe such as those performing communication based on the amplitude shiftkeying (ASK) system. Since the RFID tag based on the ASK system will notdegrade the communication sensitivity when frequency shifting occursaffected by the conductive member, unlike the tag based on the FSKsystem, so that it can ensure a highly sensitive and stablecommunication even if installed so as to contact with the conductivemember as in the present invention.

A method for installing an RFID tag as set forth in embodiments is suchthat for installing an RFID tag having an antenna coil and a controlsection to a conductive member, which comprises the steps of housing theRFID tag in a top-opened housing portion formed in the surface portionof a protective member made of a conductive material, wherein the RFIDtag has a cylindrical antenna coil to thereby have as a whole a rodshape; and housing the protective member in a top-opened installationgroove formed in the surface portion of the conductive member so as todirect the opened top of such housing portion to the opened top of suchinstallation groove, and so as to direct the axial direction of suchRFID tag in parallel to or oblique to the bottom plane of suchinstallation groove.

According to the above constitution, the RFID tag is once housed withinthe protective member, and such protective member is then housed in thetop-opened installation groove formed in the surface portion of theconductive member, so that even an extremely small RFID tag can readilybe installed in the installation groove having a conformable small size.

This saves a time required for the installation, and enablesinstallation of the RFID tag while being previously positioned in aprecise manner.

A method for installing an RFID tag as set forth in embodiments is suchthat for installing an RFID tag having an antenna coil and a controlsection to a conductive member, which comprises the steps of installingthe RFID tag, having a cylindrical antenna coil to thereby have as awhole a rod shape, so as to direct the axial direction of such tag inparallel to the installation plane of such conductive member, and so asto approximately contact with such installation plane; and performingcommunication using such RFID tag mediated by magnetic flux formed in aspace above the installation plane of the conductive member.

According to such method, the communication can be effected in a statethat the RFID tag is installed in contact with the conductive member,which is mediated by the magnetic flux penetrating the RFID tag andextending in a space over the installation plane of the conductivemember.

A communication method using an RFID tag as set forth in embodiments issuch that using an RFID tag having an antenna coil and a control sectionto a conductive member, which comprises the steps of forming aninstallation groove in the surface portion of the conductive member;installing the RFID tag, having a cylindrical antenna coil to therebyhave as a whole a rod shape, so as to direct the axial direction of suchtag in parallel to the bottom plane of such installation groove and soas to approximately contact therewith, or oblique to such bottom plane;and performing communication using by such RFID tag mediated by magneticflux formed in a space above the installation plane of the conductivemember.

According to such method, the communication is facilitated even when theconductive member is only affordable of a small-sized installationgroove, since the RFID tag having a highly size-reducible cylindricalantenna coil can be installed in such small groove.

Installing the RFID tag on the surface of the conductive memberfacilitates the attachment of such tag, and installing the RFID tagwithin the installation groove ensures the safe retainment of such tag.

As has been described in the above, installing the rod-shaped RFID taghaving a cylindrical antenna coil to the conductive member so as todirect the longitudinal direction (axial direction) in parallel to theinstallation plane and so as to approximately contact with suchinstallation plane allows communication mediated by the magnetic fluxpenetrating such RFID tag and extending in a space over the installationplane.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following description ofthe presently preferred exemplary embodiments of the invention taken inconjunction with the accompanying drawings, in which:

FIGS. 1A and 1B are a perspective view and a sectional view,respectively, explaining an exemplary installation structure of an RFIDtag of the present invention, in which a top-opened installation groovehaving a square section is formed on the installation plane of aconductive member, an RFID tag covered with a protective membercomprising a non-conductive glass container is installed in theinstallation groove, and the surface of the tag is further covered witha protective member comprising a non-conductive resin;

FIG. 2 is a front view showing a constitution of the RFID tag;

FIG. 3 is a block diagram showing a constitution of a control section ofthe RFID tag;

FIG. 4 is a schematic view showing a profile of a magnetic fieldgenerated around the RFID tag;

FIGS. 5A to 5C are schematic views showing a magnetic field generatedfrom an antenna of an external read/write terminal and reaches atop-opened installation groove formed on the installation plane of theconductive member;

FIGS. 6A and 6B are schematic views showing a magnetic field generatedfrom the RFID tag, installed in the top-opened installation grooveformed on the installation plane of the conductive member, andpropagates outward;

FIGS. 7A and 7B are a perspective view and a sectional view,respectively, showing another exemplary installation structure of anRFID tag of the present invention, in which a top-opened, arch-bottomedinstallation groove is formed on the installation plane of a conductivemember, an RFID tag covered with a non-conductive protective membercomprising a glass container is installed in the installation groove,and the surface of the tag is further covered with a protective membercomprising a non-conductive resin;

FIG. 8A is a schematic view showing still another exemplary installationstructure of an RFID tag of the present invention, in which a top-openedinstallation groove is formed on the installation plane of a conductivemember, and the surface of an RFID tag installed in the installationgroove is covered with a protective member comprising a non-conductiveresin; FIG. 8B is a plan view showing the installation groove shown inFIG. 8A alternatively having a square profile; and FIG. 8C is a planview showing the installation groove shown in FIG. 8A alternativelyhaving a round profile;

FIG. 9 is a sectional view showing an RFID tag installed in theinstallation groove so as to direct the axial direction thereof obliqueto the bottom plane of the installation groove;

FIGS. 10A and 10B are a perspective view and a sectional view,respectively, showing an installation structure in which an RFID tagcovered with a protective member comprising a non-conductive resin isinstalled on the installation plane of the conductive member;

FIG. 11 is a sectional view showing an installation structure of an RFIDtag protected on the lateral and installation planes thereof with aprotective member comprising a conductive member;

FIG. 12 is an exploded perspective view showing the installation grooveand the protective member shown in FIG. 11 alternatively having a roundprofile;

FIG. 13 is an exploded perspective view showing the installation grooveand the protective member shown in FIG. 11 alternatively having a squareprofile;

FIG. 14 is an exploded perspective view showing the RFID tag protectedon the lateral plane and/or plane opposing to the installation planethereof with a protective member which is made of a conductive materialand has at the center thereof a straight installation groove;

FIG. 15 is a view showing a result of the communication distance havingbeen measured by changing the depth of an installation groove with around profile; and

FIG. 16 is a view showing a result of the communication distance havingbeen measured by changing the diameter of an installation groove with around profile.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the installation structure of the electromagneticinduction tag, methods for installing thereof, and communication methodusing such tag according to the present invention will specifically beexplained referring to the attached drawings.

First, referring to FIGS. 1A, 1B to 6, installation structures of anelectromagnetic induction tag, methods for installing thereof, andcommunication method using such tag according to a first embodiment ofthe present invention will be explained. It should now be noted that theRFID tags preferably applicable to the embodiments described belowrelate both to those of electromagnetic coupling type andelectromagnetic induction type although the description belowspecifically deals with the latter type.

An RFID tag 1 shown in FIGS. 1A, 1B and 2 has a cylindrical antenna coil2 and a semiconductor IC chip 4 as a control section, both of whichbeing directly connected with each other without interfaced by a printedcircuit board or the like, which successfully results in size reductionof the RFID tag 1.

The single-wire-wound, cylindrical antenna coil 2 has a cylindrical coremember 3 made of iron, ferrite or so inserted therein along the axialdirection thereof (the lateral direction in FIG. 1B), in which suchantenna coil 2, core member 3, semiconductor IC chip 4 and so forth areformed in an integrated manner to provide a rod shape as a whole.

The semiconductor IC chip 4 comprises an IC (integrated circuit) chip oran LSI (large-scale integrated circuit) chip packaged in an integratedmanner, and such semiconductor IC chip 4 has incorporated therein a CPU(central processing unit) 4 a as a control section, a memory 4 b as amemory section, a sender/receiver 4 c and a capacitor 4 d as a powerstorage means, as shown in FIG. 3.

A signal sent from an antenna 9 of an external read/write terminal,shown in FIG. 5, is received by the sender/receiver 4 c, transmitted tothe CPU 4 a and converted into electric power to be stored in thecapacitor 4 d. It is now also allowable to omit the capacitor 4 d as apower storage means, and instead continuously supply electric power fromthe external read/write terminal to the semiconductor IC chip 4.

The CPU 4 a is responsible for reading out programs or various datastored in the memory 4 b, performing necessary operations and decision,to thereby enable various controls.

The memory 4 b contains various programs for allowing operation of theCPU 4 a, and various information such as history data and lot managementdata of products or parts having a conductive member 5 to which the RFIDtag 1 is provided.

The RFID tag 1 employed in this embodiment is based on thesingle-wavelength amplitude shift keying (ASK), has a wide resonancefrequency range, has an antenna coil 2 having a wire diameter as smallas several tens micrometers with or without a core member 3, and has aCMOS-IC of extremely small electric power consumption having a specificsend/receive circuit incorporated therein.

Experimental results obtained by the present inventors revealed that thecommunication using the RFID tag 1 based on the ASK system is hardlyaffected by the a conductive member placed in the vicinity thereof,since such RFID tag 1 has a wider resonance frequency range as comparedwith that of the tag based on the FSK system, and will not causereduction in received electric power, and is thus less sensitive tofrequency shifting.

From an aspect of sensitivity (communication distance), the frequencyused for the ASK wireless communication system should preferably rangefrom 50 kHz to 500 kHz, and more preferably, range from 100 kHz to 400kHz. In this embodiment of the present invention, an ASK communicationsystem of 125 kHz is used.

Experimental results obtained by the present inventors further revealedthat the magnetic field H can propagate by diffraction even out from anarrow gap, and that the RFID tag 1 can send or receive the magneticfield, which is a medium for power supply or information communication,to or from an external read/write terminal only if a fine physical gapis provided.

There are some materials possibly generate eddy current responding tothe magnetic field H generated during communication or electric powertransmission using such RFID tag 1 to thereby generate a countermagnetic flux which attenuates the initial magnetic flux; examples ofsuch conductive materials most typically include stainless steel sheet,copper sheet and aluminum sheet, and also include ferromagnetic metalssuch as iron, cobalt, nickel, alloys thereof and ferrite; paramagneticmetals such as aluminum, copper and chrome; and conductive plastics.

The lower the electric resistance of the conductive material is, thelarger the eddy current generated from the change of magnetic field H isto become. Accordingly, from an aspect of sensitivity (communicationdistance), using an iron type alloyed conductive member, such as an ironwith a relatively high electric resistance or a stainless steel, wouldbe advantageous for this invention.

As shown in FIG. 2, the RFID tag 1 having an outer diameter D₂ in theradial direction is encapsulated in a glass container 6 as anon-conductive protective member having an outer diameter D₁accommodative to D₂, which makes the whole periphery of the tagincluding the upper surface thereof is surrounded by the protectivemember.

The glass container 6 employed in this embodiment has a length L₁ in theaxial direction of approx. 7 to 15.7 mm, and an outer diameter D₁ ofapprox. 2.12 to 4.12 mm. The installation groove 7 provided to theconductive member 5 is thus formed in a size enough for accommodatingthe RFID tag 1 having the length L₁ and the outer diameter D₁. Theweight of the RFID tag 1 is approx. 55 to 400 mg.

Typical values for the length L₁ in the axial direction and the outerdiameter D₁ of the RFID tag 1; and a length L₂ in the axial directionand the outer diameter D₂ of the antenna coil 2 are listed in Table 1below.

TABLE 1 Type 1 Type 2 Type 3 Glass Length L₁ in the 12.00 mm  13.18 mm 15.90 mm  con- axial direction tainer 6 Outer diameter D₁ 2.12 mm 3.10mm 4.06 mm Antenna Length L₂ in the 6.02 mm 6.44 mm 5.78 mm coil 2 axialdirection Outer diameter D₂ 1.45 mm 1.64 mm 1.63 mm

In a typical antenna coil 2, a single copper wire having a diameter ofapprox. 30 μm is wound in a stacked form in the radial direction and ina cylindrical form in the axial direction; where an inductance of suchantenna coil 2 having the core member inserted therein was approx. 9.5mH (at 125 kHz), and an electrostatic capacity of a capacitor connectedfor resonation to the antenna coil 2 was approx. 170 pF (at 125 kHz).

The conductive member 5 has on the surface 5 a side thereof thetop-opened installation groove 7 having a square section, in which theRFID tag 1 is directly placed on the bottom plane 7 a, which is theinstallation plane of the installation groove 7, so as to align theaxial direction thereof (lateral direction in FIG. 1B) in parallel tosuch bottom plane 7 a and so as to approximately contact therewithwithout interposed with a spacer or the like.

The residual space in the installation groove 7 around the glasscontainer 6 encapsulating the RFID tag 1 is filled with a non-conductiveprotective member such as resin 8 or adhesive so as to cover the topsurface of the glass container 6. It is also allowable that the RFID tag1 is molded with a resin or covered with a plastic lid or cap, insteadof being encapsulated in the glass container 6 and fixed with the resin8.

The distance G₁ between the conductive outer surface of the antenna coil2 opposing to the bottom plane 7 a, which is an installation plane inthe installation groove 7 formed to the conductive member 5, and suchbottom plane 7 a is set at not smaller than 10 μm, which is equivalentto the thickness of an insulating film of the wound wire of the antennacoil 2, and at 5 mm or below.

While the antenna coil 2 may be projected out from the surface 5 a ofthe conductive member 5, it is more preferable to make no projection outfrom the surface 5 a in view of ensuring safe retainment of the RFID tag1.

FIG. 4 shows a profile of a magnetic field H generated from the RFID tag1 in a free state, and FIGS. 5A to 5C show profiles of a magnetic fieldH generated from an antenna 9 of an external read/write terminal andreaches the installation groove 7 provided to the conductive member 5.

The axial direction (direction of magnetic flux) of the antenna 9 andthe axial direction (direction of magnetic flux) of the antenna coil 2of the RFID tag 1 coincides with each other. FIG. 5A shows a view fromthe axial direction, FIG. 5B shows a view from a direction normal to theaxial direction, and FIG. 5C shows an enlarged view in the vicinity ofthe installation groove 7 shown in FIG. 5B.

FIGS. 6A and 6B show a profile of the magnetic field H generated fromthe RFID tag 1 embedded in the installation groove 7 of the conductivemember as shown in FIGS. 1A and 1B, where the former shows a view fromthe axial direction, and the latter shows a view from a direction normalto the axial direction.

As shown in FIG. 2, the end portion of the antenna coil 2 of the RFIDtag 1 and the end portion in the axial direction of the glass container6 are located in a positional relation defined by a dimensionaldifference between L₁ and L₂ listed in Table 1 above, and a resultantpredetermined gap, shown in FIG. 1B, formed between the lateral plane 7b of the installation groove 7 and the end portion in the axialdirection of the antenna coil 2 facilitates the formation of themagnetic flux loop penetrating such antenna coil 2, which contributesthe formation of the magnetic field H.

The magnetic field H is formed by the leakage magnetic flux on thesurface side of the conductive member 5 as shown in FIGS. 6A and 6B alsowhen the RFID tag 1 is directly installed on the bottom plane 7 a of thetop-opened installation groove 7 so as to approximately contacttherewith.

The magnetic field H can propagate by diffraction only when an openingof the installation groove 7 is given as a narrow gap provided that aproper length L₂ in the axial direction of the antenna coil 2 isensured, and this allows the RFID tag 1 to send or receive AC magneticfield, which is a medium for power transmission and informationcommunication, to or from an external read/write terminal not shown.

According to such constitution, a part of the magnetic flux, goes outfrom the end portion of the cylindrical antenna coil 2 and extends inthe axial direction, penetrates into the conductive member 5, and isslightly attenuated in the total strength due to eddy current induced insuch conductive member 5, but a part of the residual magnetic flux canform a loop routing through the RFID tag 1 and a space over theinstallation plane of the conductive member 5, which can mediate thecommunication with an external read/write terminal.

The RFID tag 1 having the highly size-reducible cylindrical antenna coil2 is beneficial since such tag 1 can readily be installed when only anextremely limited space is available for the installation.

Another benefit resides in a good operability since the communication ismediated by the magnetic flux penetrating the RFID tag 1 and extendingin a space over the installation plane of the conductive member 5.

FIGS. 7A and 7B show another exemplary installation groove 7 formed inthe conductive member 5 by a more simple process. In the installationpreviously shown in FIGS. 1A and 1B in which an approximatelyrectangular parallelepiped groove is formed, fabrication of theconductive member 5 requires a preliminary consideration on the shapethereof so as to afford such groove, or the installation groove 7 ispossibly formed by drilling a plurality of holes aligned side by side.

Fabrication process for such installation groove 7 as shown in FIGS. 1Aand 1B is, however, labor-consuming in particular for the case that theRFID tag 1 is to be installed to an already-finished conductive member5. On the contrary, the installation groove 7 shown in FIGS. 7A and 7Bhaving an arched bottom can be formed by cutting the conductive member 5using a milling machine or lathe. The RFID tag 1 can directly be housedtherein and installed so as to approximately contact with the bottomplane 7 a of such installation groove 7, and the residual space in theinstallation groove 7 around the RFID tag 1 is filled with anon-conductive protective member such as resin 8 or adhesive so as tocover the outer periphery including the top surface of the tag.

This is advantageous in the simplicity of the process for forming theinstallation groove 7, in particular for the case that the RFID tag 1 isinstalled to the conductive member 5 of an already-finished product.

According to such constitution, only a shallow installation groove 7will suffice so that properties and strength of the conductive member 5can desirably be retained. This is particularly advantageous when theRFID tag 1 has to be installed to a thin conductive member 5.

Hence, according to the present invention, it is no more necessary,unlike the conventional installation, to ensure a space between the RFIDtag 1 and the conductive member 5, or to interpose a spacer or the likemade of a non-conductive member, so that the installation groove 7 to bemade to the conductive member 5 can be shallower and the installationstructure can be more simple.

FIGS. 8A to 8C show an installation structure in which the antenna coil2 and the semiconductor IC chip 4, both in a bare state without beingencapsulated in a glass container, are embedded in the installationgroove 7. Such omission of the glass container will not cause anyproblem provided that proper electric insulation is ensured by anelectrical insulating film of the antenna coil 2 and a package of thesemiconductor IC chip 4. This promotes further size reduction of a spacefor installation groove 7, to thereby retain properties and strength ofthe conductive member 5.

The top-opened installation groove 7 to be formed in the conductivemember 5 may have a square section as shown in FIG. 8B, or may have around section as shown in FIG. 8C. The installation groove 7 having around section is advantageous since such groove 7 can readily be formedby, for example, drilling.

Shown in FIG. 15 is a measured result regarding the relation between thechange of communication distance and the depth of the installationgroove 7 with a round profile as illustrated in FIG. 8A.

The RFID tag used in this case is a reading only type (model typeUNIQUE) made from Sokymat of Switzerland. Such RFID tag is a cylindricalantenna coil having a copper wire wound around a rod shape core and isenclosed in a glass container, in which the length of the core is 7.92mm, the diameter of the coil is 1.42 mm, and the diameter of the glasscontainer is 2.12 mm. This experiment was performed in a state where theglass container is cut to expose a tip end portion of the core.

The measuring method is performed by forming a hole with a diameter of12.45 mmφ upon an iron block so as to form the installation groove 7,arranging the RFID tag horizontally inside the hole, and arranging areading device above the hole.

Used as the reading device is a pocket reader (model type rdr 100) madefrom I.D. Systems Inc., in which the distance between thesending/receiving surface of the antenna and the hole is measured as thecommunication distance.

Adjustment of depth is performed by placing a thin iron plate cut into around shape upon a bottom of the hole and changing the number of theplates.

As apparent in FIG. 15, when the depth is 8 mm, the communicationdistance is 0 mm (in other words, a state where the sending/receivingsurface is contacting to the hole), and when the hole is formed with adepth no less than such depth, communication could not be performed.Further, the shallower the hole is formed, the longer the communicationdistance tends to become.

However, when the installation groove 7 is formed too shallow, the RFIDtag would project outward from the groove and would be undesirable interms of protection. Accordingly, the maximum depth of the hole shouldpreferably be determined by the distance for obtaining a desiredcommunication distance, and the minimum depth thereof should preferablybe determined by the diameter of the RFID tag. The suggested range forthe depth of the hole is approximately 1.1 times through 3 times of thediameter of the RFID tag.

Next, shown in FIG. 16 is a measured result regarding the relationbetween the communication distance and the diameter of a hole having adepth of 3 mm. The RFID tag, the reading device, the method, and thelike used for measurement are the same as those in FIG. 15.

As apparent in FIG. 16, although the communication distance tends toexpand when the diameter of the hole is extended, the change from suchextension is relatively small. Accordingly, when the installation grooveportion 7 is of a round profile, it would be sufficient for the diameterthereof to be slightly larger than the length of the RFID tag, and froma practical aspect, the diameter of the hole is desired to beapproximately 1.1 times through 1.5 times of the length of the RFID tag.

FIG. 9 shows an exemplary installation in which the RFID tag 1 isinstalled so as to align the axial direction thereof oblique to thebottom plane 7 a of the installation groove 7. According to suchconstitution, the projected area for the installation on the conductivemember 5 can further be reduced as compared with the case for the aboveembodiments. In addition, the magnetic flux can leak through a spaceresulted from such oblique installation toward the outside of theinstallation groove 7, which can mediate the communication with anexternal read/write terminal.

FIGS. 10A and 10B show an exemplary installation, in which the outerperiphery including the top surface of the RFID tag 1, which comprisesthe antenna coil 2, core member 3 and semiconductor IC chip 4, is moldedwith a resin 8 as a non-conductive protective member, and such tag 1 isfixed as contacted on the surface 5 a of the conductive member 5 usingmachine screws 10 so as to align the axial direction thereof in parallelto such surface 5 a as an installation plane.

It is now also allowable to use an adhesive or so, in place of themachine screws 10, for the fixation, and it is even allowable to fix theantenna coil 2 and the semiconductor IC chip 4 in a bare state on thesurface 5 a of the conductive member 5.

Also in this embodiment, the distance G₁ between the conductive outersurface of the antenna coil 2 opposing to the conductive member 5, andthe surface 5 a of such conductive member 5 as an installation plane isset at not smaller than 10 μm, which is equivalent to the thickness ofan insulating film of the wound wire of the antenna coil 2, and at 5 mmor below.

According to such constitution, it is no more necessary to form theinstallation groove 7 to the conductive member 5 unlike the foregoingembodiments, which is advantageous in retaining properties and strengthof the conductive member 5. Enhancing the strength of a case coveringthe antenna coil 2 and the semiconductor IC chip 4 will ensure saferetainment of the RFID tag 1.

FIGS. 11 to 14 show exemplary installations in which the lateral planeand a plane opposing to the installation plane of the RFID tag 1 areprotected with a protective member 11. The protective member 11 shown inFIG. 12 is composed as a metal protective member comprising acylindrical side plate 11 a and a disk-formed bottom plate 11 b, bothhaving a size conformable to the RFID tag 1, and the top-openedinstallation groove 7 formed in the conductive member 5 is composed tohave a round section in a size conformable to such protective member 11.

The protective member 11 shown in FIG. 13 comprises a square side plate11 a and a square bottom plate 11 b, both having a size conformable tothe RFID tag 1, and the top-opened installation groove 7 formed in theconductive member 5 is composed to have a square section in a sizeconformable to such protective member 11. The protective member 11 canbe composed of various metals such as iron, brass and stainless steel.

The RFID tag 1 is housed in the top-opened housing portion of theprotective member 11, and fixed by covering the outer peripheryincluding the top surface thereof with a protective member which may becomposed of a non-conductive material such as resin 8 or adhesive.

Also in this embodiment, the distance G₁ between the conductive outersurface of the antenna coil 2 opposing to the conductive member 5, andthe bottom plate 11 b of such protective member 11 as an installationplane is set at not smaller than 10 μm, which is equivalent to thethickness of an insulating film of the wound wire of the antenna coil 2,and at 5 mm or below.

An adhesive 12 is applied on the lateral plane and the bottom plane ofthe protective material 11, or on the inner plane of the installationgroove 7 of the conductive member 5; the protective member 11 isinserted in the installation groove 7 so as to direct the opened top ofsuch housing portion to the opened top of such installation groove 7 andis then fixed by the adhesive 12 to thereby complete the installation.The RFID tag 1 in this case is installed so as to align the axialdirection thereof in parallel to or oblique to the bottom plane 7 a ofthe installation groove 7 as shown in FIG. 9.

It is now allowable to preliminarily apply the adhesive 12 on at leasteither one of the protective member 11 or the installation groove 7 ofthe conductive material 5.

While this embodiment illustratively showed an exemplary installation inwhich all of the top plane 11 a ₁, of the side plate 11 a of theprotective member 11, the top surface of the resin 8 and the surface 5 aof the conductive material 5 are approximately aligned in the sameplane, the top surface 11 a ₁ of the side plate 11 a of the protectivemember 11 may be fixed so as to be projected upward from the surface 5 aof the conductive member 5.

A predetermined gap is formed between the end portion of the core member3 inserted in the antenna coil 2 of the RFID tag 1 and the inner plane11 a ₂ of the side plate 11 a of the protective member 11, whichfacilitates formation of the magnetic flux penetrating the antenna coil2 and accordingly the formation of magnetic field H.

The magnetic field H can propagate from the opened top portion of theprotective member 11, which allows send/receive operation of AC magneticfield, which is a medium for power transmission and informationcommunication, between the RFID tag 1 and an external read/writeterminal not shown.

According to such constitution, the RFID tag 1 is housed within theprotective member 11, and such protective member 11 covering the lateralplane and a plane opposing to the installation plane of the RFID tag 1is fixed within the installation groove 7 of the conductive member 5,which ensures safe retainment of the RFID tag 1.

Since the RFID tag 1 is installed in the installation groove 7 of theconductive member 5 while being housed within the top-opened protectivemember 11, the magnetic field H, which is a medium for powertransmission and information communication, can be sent to or receivedfrom an external read/write terminal with a high sensitivity mediated bythe magnetic flux in a space over the installation plane of theconductive member 5.

Composing the protective member 11 in a container form, having the sideplate 11 a and the bottom plate 11 b, allows protection of the lateralside of the RFID tag 1 by such side plate 11 a, and protection andreinforcement of a plane of the RFID tag 1 opposing to the installationplane with such bottom plate 11 b. Preliminarily filling the resin 8into such container composed of the side plate 11 a and the bottom plate11 b can facilitate the fixing of the RFID tag 1 to the protectivemember 11.

Providing a shock absorbing material within the housing portion of theprotective member 11 for housing the RFID tag 1 can effectively absorbimpact by external force, to thereby ensure safe retainment of the RFIDtag 1. Providing a heat insulating material, on the other hand, canstabilize the temperature of the RFID tag 1, to thereby prevent theresonance frequency from being shifted, and stabilize the send/receiveoperation of electric power and signals.

Previously housing and fixing the RFID tag 1 in the housing portion ofthe protective member 11 facilitates the attachment of such protectivemember 11 and positioning of the RFID tag with respect to the conductivemember 5.

FIG. 14 shows an exemplary installation in which the cylindricalprotective member 11 made of a conductive material has on the surfaceside thereof a straight groove 11 c as a housing portion, and the RFIDtag 1 is housed in such groove 11 c so as to align the axial directionthereof in parallel to the installation plane of such groove 11 c and soas to keep a distance of 10 μm to 5 mm away from such installationplane, to thereby protect the lateral plane and a plane opposing to theinstallation plane of the RFID tag 1 with such protective member 11.

An adhesive 12 is applied on the lateral plane and the bottom plane ofthe protective material 11, or on the inner plane of the installationgroove 7 of the conductive member 5; the protective member 11 isinserted in the installation groove 7 so as to direct the opened top ofsuch housing portion upward, and is then fixed by the adhesive 12 tothereby complete the installation.

While being not illustrated in the drawings, the RFID tag 1 may beinstalled in the installation groove 7 having a conformable size buthaving a variety of shapes, or the protective member 11 having a sizeconformable to the RFID tag 1 but having a variety of shapes may beinserted and fixed in the installation groove 7 having a conformableshape.

It is also allowable to pack a non-conductive shock absorbing materialor a heat insulating material such as sponge or glass wool in theresidual space within the installation groove 7 or in the protectivemember 11 around the RFID tag 1 housed therein, and to further cover thesurface thereof with the resin 8 or the like.

The foregoing description of a preferred embodiment of the invention hasbeen presented for purposes of illustration and description, and is notintended to be exhaustive or to limit the invention to the precise formdisclosed. The description was selected to best explain the principlesof the invention and their practical application to enable othersskilled in the art to best utilize the invention in various embodimentsand various modifications as are suited to the particular usecontemplated. It is intended that the scope of the invention not belimited by the specification, but be defined by the claims set forthbelow.

1. A structure for mounting an RFID tag onto a conductive member,comprising: an RFID tag, that includes a cylindrical antenna coil and acontrol section, that communicates using amplitude shift keying (ASK); acontainer made of a non-conductive material that encloses the RFID tag,such that a longitudinal direction of the cylindrical antenna coil issubstantially aligned with a longitudinal direction of the container,and insulates the RFID tag from the conductive member; a groove formedwithin a top surface of the conductive member, wherein interiordimensions of the groove substantially correspond to external dimensionsof the container; and a non-conductive protective member made withnon-conductive material that covers the top surface of the container;wherein the longitudinal direction of the cylindrical antenna coil isaligned substantially parallel with the top surface of the conductivemember.
 2. The installation structure for an RFID tag according to claim1, wherein a distance between a surface of the groove in the conductivemember and the RFID tag enclosed within the container is from about 10μmto about 5 mm.
 3. The installation structure for an RFID tag accordingto claim 1, further comprising: a conductive protective member that is alayer of conductive material positioned between the container and asurface of the groove.
 4. The installation structure for an RFID tagaccording to claim 3, wherein the conductive protective member is anopen housing of conductive material that receives the container andinserts within the groove.
 5. The installation structure for an RFID tagaccording to claim 1, wherein a frequency used for ASK communication isfrom about 50 kHz to about 500 kHz.
 6. A method for installing within aconductive member an RFID tag, that includes a cylindrical antenna coiland a control section, that is enclosed in a container made of anon-conductive material such that a longitudinal direction of thecylindrical antenna coil is substantially aligned with a longitudinaldirection of the container and such that the RFID tag is insulated fromthe conductive member; forming a top-opened installation groove in a topsurface of the conductive member; installing the container in an openhousing of a conductive protective member made of a conductive material;disposing the conductive protective member in the top-openedinstallation groove formed in the top surface of the conductive member,an opening of the conductive protective member being accessible throughthe top surface of the conducting member, whereby the longitudinaldirection of the cylindrical antenna coil enclosed within thenon-conducting container is aligned substantially in parallel with thetop surface of the conductive member.
 7. A communication method using anRFID tag installed within a conductive member, wherein the RFID tagcommunicates with an amplitude shift keying (ASK) system via acylindrical antenna coil that includes a control section, and whereinthe RFID tag is enclosed within a container made of non-conductingmaterial such that a longitudinal direction of the cylindrical antennacoil is substantially aligned with a longitudinal direction of thecontainer and the RFID is insulated from the conductive member, themethod comprising: forming a top-opened installation groove in a topsurface of the conductive member; installing the container within theinstallation groove, such that the longitudinal direction of thecylindrical antenna coil enclosed within the non-conducting container issubstantially aligned in parallel with the top surface of the conductivemember; and communicating using RFID via magnetic flux mediated by theRFID above the top surface of the conductive member.